This application is a proposal to study the photophysics and photochemistry of a number of chromophores that are present in the organic soluble portion of human retinal lipofuscin. This extract has been shown by several groups including ours to be efficient at photosensitizing highly reactive intermediates such as free radicals, singlet oxygen and superoxide. The chromophores to be studied absorb light in the wavelength region that is transmitted to the retinal and therefore their ability to act as photosensitizers has a direct impact on light induced damage to the retinal. Initially the work focuses on two chromophores whose structures are known, one being the major fluorescent component of human retinal lipofuscin and the other its likely precursor. Their potential role in exacerbating photooxidative stress on the retinal will be ascertained by examining the formation and fate of excited singlet and triplet states and the resultant reactive species. This will be achieved through the use of both steady state and time resultant photochemical techniques that allow the step-by-step mechanisms of these processes to be directly observed. These materials will be studied in model biological environments (micelles, liposomes, erythrocyte ghosts) to more closely approximate the native environment. These data may also allow for quantitative, non-invasive measurements of these chromophores in vivo. Finally, action spectra for the formation of these reactive intermediates will be recorded in order to determine other possible compounds present in human retinal lipofuscin that are potential photooxidizing agents. Information from these studies may allow for the development of protocols to slow down or stop the processes that lead to irreversible damage to the human retina